All but the simplest of electronic devices utilize nonvolatile memories. When an electronic device must retain information during and after being placed in an unpowered state, nonvolatile memories must be provided. Several types of nonvolatile memories are known in the art. Nonvolatile memories may be portable, auxiliary, or integrated in a circuit, or as a component, in both general and embedded computer systems. Most generally, nonvolatile memories are found in digital cameras, cellular telephones, music players, and as the key component in portable memory devices (e.g. USB based flash drives).
Nonvolatile memory is often formed using electrically-erasable programmable read only memory (EEPROM) technology. EEPROM, also known as flash memory, uses an architecture that is inadequate in its access, erase and write times, for the increasing operational speed requirements and decreasing size requirements of electronic devices. A memory architecture with faster access, erase and write times scalable to smaller devices is needed. Volatile memories (such as Random Access Memory (RAM)) are fast and inexpensive. Nonvolatile memories must improve before they can become a successful replacement in applications currently using volatile flash memories. Resistive switching memories are a type of nonvolatile memory which may provide an alternative to flash memories.
Resistive switching nonvolatile memories are formed of arrays of resistive switching memory with resistive switching elements where each element has two or more stable resistive states. Bi-stable resistive switching elements have two stable states. The application of an electric field having a particular voltage or current results in a desired element resistance. Voltage pulses are typically used to switch the memory element from one resistance state to the other.
Resistive switching elements use a “forming process” to prepare a memory device for use. The forming process is typically applied at the factory, at assembly, or at initial system configuration. A resistive switching material is normally insulating, but a sufficient voltage (known as a forming voltage) applied to the resistive switching material will form one or more conductive pathways in the resistive switching material. Through the appropriate application of various voltages (e.g. a set voltage and reset voltage), the conductive pathways may be modified to form a high resistance state or a low resistance state. For example, a resistive switching material may change from a first resistivity to a second resistivity upon the application of a set voltage, and from the second resistivity back to the first resistivity upon the application of a reset voltage.
To function properly, a resistive switching element must have two well defined resistive states. Therefore, it would be advantageous if a method existed for determining predictable switching behavior in a resistive switching element.